1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method capable of continuing image formation without stopping a document reading process even when multiple documents are fed in an overlapped manner at the time of feeding a document.
The present invention also relates to an image forming apparatus and an image forming method capable of reducing the burden of the user and continuing image formation even when sheets on which images are to be formed are fed in an overlapped manner.
2. Description of Related Art
In recent years, an image forming apparatus such as a digital complex machine having a scanner function, a printer function, and a facsimile function comprises an automatic document reading apparatus, and processes a large amount of documents at high speeds by feeding one sheet of document at a time from a stack of documents placed on a document tray of the automatic document reading apparatus to an image reading unit, reading an image recorded on the document, and performing a process such as printing on recording paper based on the read image.
However, when feeding a document by the automatic document reading apparatus, overlapped feeding in which two or more sheets of documents are fed in an overlapped manner may sometimes occur because the apparatus may fail to separate and feed one sheet of document at a time due to the influence of humidity or static electricity at the time of feeding the document. Conventionally, when overlapped feeding occurs in an image forming apparatus, the feed of the documents is stopped, and image forming processes such as an exposure process, a development process, a transfer process and a fixing process are also stopped. Therefore, there is a problem that the job efficiency of the image forming processes is decreased, or a problem that a lot of burden is placed on the user to perform a recovery process when overlapped feeding occurs. Hence, there were proposed image reading apparatuses and image forming apparatuses capable of taking appropriate measures when overlapped feeding occurs.
For example, there was proposed a facsimile machine in which image data about each page of a document obtained by reading and scanning the document is stored in an image memory, and, when overlapped feeding is detected at the time of reading a document, the contents of the image data stored in the image memory are printed on recording paper, and thus the user who sees the contents of the image data can easily determine which page of documents was not read nor scanned (see, for example, Japanese Patent Application Laid-Open No. 06-303375 (1994)).
Moreover, there was proposed an image reading apparatus in which, when overlapped feeding is detected at the time of reading a document, marking is added to the surface of the overlapped documents, so that documents which were read and documents which have not been read are easily distinguished from each other (see, for example, Japanese Patent Application Laid-Open No. 08-91630 (1996)).
There was also proposed an image reading apparatus in which, when overlapped feeding is detected at the time of reading a document, the overlapped documents and documents that were not fed in an overlapped manner are sorted from each other and discharged separately, and therefore, even when overlapped feeding occurs, it is possible to reduce the operational burden of the operator by continuing to feed documents without stopping, collecting only documents failed for reading due to overlapped feeding after completion of reading the documents, and performing the reading operation again (see, for example, Japanese Patent Application Laid-Open No. 2000-165594).
Further, in recent years, image forming apparatuses, such as a printer or a digital copying machine having a scanner function, a printer function and a facsimile function, can process a large volume of data at high speeds by performing a printing process on recording paper, based on image data transmitted from an external personal computer, or image data stored in a memory device such as a HDD beforehand.
However, when feeding the recording paper from a paper feed cassette to perform the printings process on the recording paper, overlapped feeding in which two or more sheets of recording paper are fed in an overlapped manner without separating and feeding the recording paper one sheet at a time may sometimes occur due to the influence of humidity or static electricity. Conventionally, when overlapped feeding occurs in the image forming apparatus, the feed of the recording paper is stopped, and image forming processes such as an exposure process, a development process, a transfer process and a fixing process are also stopped. Therefore, there is a problem that the job efficiency of the image forming processes is decreased, or a problem that a lot of burden is placed on the user to perform a recovery process when overlapped feeding occurs. Hence, there was proposed an image forming apparatus capable of taking appropriate measures when overlapped feeding occurs.
For example, there was proposed an image forming apparatus in which, when overlapped feeding is detected in feeding recording paper, the recording paper involved in overlapped feeding is discharged as it is onto a specified tray without forming an image, image data supposed to be formed on the recording paper is saved, and an image is formed based on the saved image data on recording paper supplied from a recording paper supply section, and thus it is possible to ensure continuity of image forming processes and reuse the recording paper involved in overlapped feeding (see, for example, Japanese Patent Application Laid-Open No. 2002-333797).
Further, there was proposed an image forming apparatus for creating a bunch of paper with an insertion paper inserted between sheets of recording paper, in which when sheets of the insertion paper are fed in an overlapped manner, a bunch of paper created normally and a bunch of paper which was not created normally due to overlapped feeding are discharged separately onto different discharge trays (see, for example, Japanese Patent Application Laid-Open No. 2003-327361).
In addition, there was proposed an image forming apparatus in which, when overlapped feeding is detected at the time of feeding transfer paper, the image creating conditions such as a fixation temperature or transfer conditions are changed according to an overlapped feeding detection value, such as the thickness of the transfer paper or the length of the transfer paper in the transport path direction, and therefore, even when overlapped feeding occurs, it is possible to perform image formation without stopping a printing operation (see, for example, Japanese Patent Application Laid-Open No. 2005-15166).